Double bond isomerization, i.e., the shifting of the position of a double bond in an olefinic compound, is a well known phenomenon. Such an operation is frequently valuable in the conversion of one olefinic compound to one or more isomers thereof which may be less plentiful and more valuable. Olefinic compounds as a class are useful in themselves, such as for use as monomers to produce a wide variety of polymeric compositions, or for use as building blocks to prepare other still more valuable compounds.
A number of catalysts are known in the art to be active in double bond isomerization. However, such double bond isomerization is frequently accompanied by undesirable side reactions, such as for example, cracking, dehydrogenation, polymerization, and the like.
One use to which double bond isomerization catalysts have been put is as one component of a mixed disproportionation catalyst composition. The disproportionation, or metathesis, of olefins is a reaction in which one or more olefinic compounds are transformed into other olefins of different molecular weights. The addition of double bond isomerization catalysts thereto has been shown to increase the disproportionation activity of the disproportionation catalyst component.
By the term "disproportionation" or "metathesis" throughout this specification is meant the conversion of the feed olefinic (or unsaturated) hydrocarbon to a mixture of olefinic (or unsaturated) hydrocarbons having different numbers of carbon atoms than the feed hydrocarbons. The disproportionation of an olefin with itself to produce an olefin of a higher molecular weight and an olefin of a lower molecular weight can also be referred to as self-disproportionation. For example, propylene can be disproportionated to produce ethylene and cis-, and trans-2-butene. Another type of disproportionation involves the cross-disproportionation of two different olefins to form still another olefins. An example of the latter would be the reaction of one molecule of 2-butene with one molecule of 3-hexene to produce two molecules of 2-pentene.
While many catalyst compositions are known in the art for olefin disproportionation, it is a continuing objective of those of skill in the art to provide catalyst compositions having improved productivity, i.e., increased conversion of starting material and/or increased selectivity to the desired reaction product.
The present invention is based upon the discovery of novel double bond isomerization catalysts as well as the discovery of a way to dramatically improve the activity of disproportionation catalysts.